The present invention relates to an improved pinch valve for controlling the flow of fluid. More particularly, the invention concerns a self-pressurizing pinch valve for controlling the flow of fluid under pressure.
In liquid filling machines for dispensing predetermined quantities of liquid into containers, for example, valves are generally provided for controlling the flow of the liquids. When the liquids being dispensed must be of high purity, as in the case of medicines, for example, the valves employed in the filling machines must be carefully selected so as not to cause contamination problems, e.g. present cracks or seams or additional surfaces where the material being dispensed may become trapped. Contamination problems may become particularly serious where it is necessary to successively dispense different materials which must be of high purity from the same filling machine. Some filling machines may be steam cleaned after dispensing a first liquid material but if the first liquid material is trapped in cracks or seams about a valve the steam cleaning may not remove all of the first material. Thus a second material dispensed from the machine can become contaminated.
Pinch valves for controlling the flow of fluids are known. These valves generally include a flexible hose or sleeve through which a fluid is conveyed The flexible hose is pinched to reduce or stop the flow therethrough. Pinching of the hose may be accomplished by applying high pressure fluid about the outside of a portion of the hose, by mechanically compressing the hose, or by twisting the hose, etc. From the standpoint of reducing or eliminating contamination problems in liquid filling machines, pinch valves may be particularly advantageous in that the flexible hoses provide smooth and unobstructed passages for liquid flowing through the valve so as to avoid or minimize the additional surfaces, cracks or seams that could trap material. However, pinch valves can be problematical where fluids to be controlled are under high pressure. That is, the flexible hose of a pinch valve may be unduly distended or burst as a result of the high internal pressure. In order to avoid these problems it is known to provide a pressurized fluid about the outside of the flexible hose to minimize differential pressures on the hose or sleeve as in U.S. Pat. No. 4,108,418, for example. If the fluid pressure in the flow line varies significantly, it is necessary to adjust the pressure around the flexible hose to maintain a substantial balance of the internal and external pressures to prevent unwanted collapse or expansion of the sleeve In the case of manual control, this necessitates a time consuming monitoring of the pressure in the flow line and manual adjustment of the pressure supplied to the area about the flexible hose. However, the technique of visually monitoring the flow line pressure and manually adjusting the fluid pressure provided about the flexible hose is a time consuming process and may be unacceptable since a busy operator may forget to make the necessary adjustment or, where the pressure changes vary considerably in short periods of time, it is not possible for the operator to keep up with the necessary adjustments.
One prior art attempt to avoid these problems is suggested in U.S. Pat. No. 3,329,390 wherein a variable orifice valve is provided with a flexible hose or sleeve which is twisted for adjusting the flow of fluid therein. In this known valve, a pressure equalizing passageway is provided which communicates the fluid passage upstream of the flexible sleeve with a sealed annular space around the exterior of the sleeve so as to balance the pressure across the sleeve thereby preventing collapse of the sleeve due to pressure drops resulting from a restriction effected by the twisting of the hose. While this arrangement is suitable for controlling the flow of certain gases, if liquids are passing through the flow line it may be undesirable to allow the liquids to leave the flow line by way of the pressure equalizing passageway. Further, such a system may not function properly with high viscosity liquids. Moreover, this known valve is unacceptable where liquids of high purity are to be dispensed because of the contamination problems posed by the entrapment of liquid in the pressure equalizing passageway and the sealed annular space around the exterior of the sleeve. Steam cleaning would not effectively clean these areas without disassembly of the valve.
An object of the present invention is to provide a pinch valve which is suitable for controlling the flow of high pressure fluids, particularly liquids, which avoids the aforementioned disadvantages of the known valves. More particularly, an object of the invention is to provide a pinch valve which can be used for controlling the flow of fluids under pressure without requiring the constant attention of the operator and where the fluid pressures may vary significantly in short periods of time. A further object of the invention is to provide in a liquid filling machine for dispensing predetermined quantities of liquid which must be of high purity, a self-pressurizing pinch valve which avoids the contamination problems of the type referred to above.
These and other objects of the present invention are attained by providing a self-pressurizing pinch valve comprising flexible hose means for conveying a fluid, chamber means about at least a portion of the flexible hose means, the flexible hose means being adapted to be pinched in the chamber means for valving the flow of fluid therethrough, and means responsive to movement of the flexible hose means for controlling the pressure in the chamber means so that it substantially balances the internal pressure in the hose means.
According to a disclosed, preferred embodiment of the invention the means for controlling the pressure in the chamber means increases the pressure in the chamber means in response to radial expansion of the flexible hose means and decreases the pressure in the chamber means in response to radial contraction of the flexible hose means.
The means for controlling the pressure in the chamber means includes a valve means for controlling fluid communication between the chamber means and a source of pressurized fluid. The valve means is actuated in response to movement of the flexible hose means. In particular, a member drivingly associated with the valve means is positioned for movement adjacent an outer surface of the flexible hose means such that radial expansion of the hose means with increasing internal hose pressure causes the valve means to open and permit pressurized fluid from the source to enter the chamber means. The member drivingly associated with the valve means is a piston which is positioned adjacent the hose means in an additional chamber means in fluid communication with the chamber means.
According to a further feature of the invention, the means for controlling the pressure in the chamber means includes an outlet for releasing pressurized fluid from the chamber means. The outlet is closed by the flexible hose means when the pressure in the chamber means is less than or substantially equal to the internal pressure in the hose means and opened when the fluid pressure in the chamber means is substantially greater than the internal pressure in the hose means so as to radially compress the hose means.
The self-pressurizing pinch valve of the invention, when used with a solenoid actuated valve body, for example, for pinching the flexible hose means, results in a fast acting pinch valve suitable for use in liquid filling machines which does not pose unacceptable or undesirable contamination problems and which can be used to dispense fluids at low or high, variable pressures without necessitating the attention of the machine operator.
These and other objects, features and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawings, which show, for purposes of illustration only, one embodiment in accordance with the present invention .